The Incredible Explosion of Dog Breeds

by Remy Melina | August 05, 2010 04:02am ET

From a teacup-size Chihuahua to a Great Dane, there is an incredible
amount of variety among dog breeds. But all breeds belong to a single
species, so scientists have studied the breeds to better understand the
workings of evolution, and how such great variation could have arisen
within one group.

The dog (Canis lupus familiaris) is far more variable in size, shape
and behavior than any other living mammal, but most experts now believe
that all dogs, no matter how
different, originated exclusively from a single species: the gray wolf
(Canis lupus) of central Asia, said James Serpell, professor at the
University of Pennsylvania School of Veterinary Medicine and editor of
"The Domestic Dog: Its Evolution, Behaviour, and Interactions With
People" (Cambridge University Press, 1995).

It's also likely that there was just one domestication event, and all
domesticated dogs today descended from an ancestral wolf-dog that
became someone's best friend long ago. The evidence comes from a 2009
study in which a team of researchers at the Royal Institute of
Technology in Stockholm analyzed samples of mitochondrial DNA (the DNA
found in mitochondria, or energy-making structures within cells) from
dogs around the world.

They found that all dogs belong
to one lineage, which indicates that domestication occurred just
one time. (If wolves were domesticated several times in various regions,
the team would expect to find more than one lineage among modern dogs.)

Despite the fact that dogs were first domesticated about 14,000 to
17,000 years ago, most dog breeds were developed within the last few
centuries. When ancient humans bred dogs for features such as a louder
bark (for added protection of their owner's property) or a docile
temperament (so it would be less likely to lash out at its owner), they
were actually already tinkering
with the selection of dog genes.

One of the earliest breeds believed to be purposefully selected for
its preferred traits is still around today – the greyhound. Perhaps the
first fully distinct breed was the Saluki, also called the Arabian
greyhound, whose name translates to "noble," according to "Simon &
Schuster's Guide to Dogs" (Fireside, 1980).

"Selective cross-breeding has been done since antiquity, but it
really accelerated during the 19th century," said Leslie Irvine of the
University of Colorado at Boulder, who is author of "If You Tame Me:
Understanding Our Connection with Animals" (Temple University Press,
2004).

Over time, because of natural mutations, climate and human
preferences, "breeds became ever more numerous and specialized until
they reached the point of modern classification," according to "Guide to
Dogs." This classification is based on the aptitude of a breed in five
skills: hunting, shepherding, guarding, work and company.

Now, there are about 340 breeds recognized by the Fédération
Cynologique Internationale (FCI), the world governing body of dog
breeds, sometimes known as the World Canine Organization. But the
standards for breed recognition vary from country to country – the
American Kennel Club currently recognizes only 167 breeds.

Recently, the number of deliberately
crossbred "designer dogs" has been growing. These include the
labradoodle (a cross between a Labrador and a poodle), the cockapoo (a
cross between a cocker spaniel and a poodle) and the puggle (the
offspring of a pug and a beagle).

"Dogs are constantly evolving as we're continually building variants
of dog breeds," said Stanley Coren, author of "The Modern Dog" (Free
Press, 2008).

"The nature of humans is to want unique things, but a unique thing is
not necessarily a better thing," Coren told Life's Little Mysteries.